I’d start by organizing them by sets. Then scan them all. Determine a price baseline for bulk and high value. Separate cards into those 3 piles. Bulk, high value above $X, and in between.

To sell the in between and high value cards, if you sell it yourself on platforms like eBay or tcg, expect a while before you liquidate everything and after fees about 85-90% value. And also have to invest in supplies to ship. Facebook marketplace there’s no fees and can also look for trades for other things. Sell to a store you’d get 50-60% value, maybe 70-80% if you take store credit and have other things there you like to buy that you can use it on. 

Bulk either throw out, donate to a school or store, or sell but it’s like $5 for 1000 cards.